Current wireless communication methods typically employ the use of an omni-directional antenna in a device for transmitting and receiving data. When the device uses the omni-directional antenna to transmit a data packet into a wireless medium, the transmission is of a broadcast nature since the transmission is typically transmitted in equal strength in every direction. However, one problem with using the omni-directional antenna is that the antenna typically limits the range of the device. For example, in a star-topology network, slave devices may be assumed to be in omni-directional transmission range of a master device since they are associated with the master device but the peer slave devices may be unable to communicate directly with each other despite the fact that they are in the same network.
One method to overcome the range limitation is to increase the transmission power of the transmitting device such that the transmission may reach an intended receiving device that was originally out of range. One problem may arise since increasing the transmission power typically increases the power consumption of the transmitting device. This may be disadvantageous for a battery-powered device with limited power resources. Another problem that may arise with increasing transmission power to increase range is that increasing transmission power typically increases the interference range. In other words, there may be increased interference with potential communication between other devices that were originally out of range of the transmitting device.
Another method to overcome the range limitation is typically to use multi-hop communication to relay data packets. However, one problem that may arise when multi-hop communication is used is that performance typically suffers since latency between the transmitting device and receiver device typically increases when relaying data packets during multi-hop communication. Another problem that may arise when using multi-hop communication is that assistance is typically required of one or more relaying devices. This typically prevents the relaying devices from transmitting their own communication and also typically increases their overall power consumption when relaying is carried out. Yet another problem that may arise when using multi-hop communication is that having the same data packet transmitted and then relayed one or more times typically causes inefficiency as the wireless medium access resource may be consumed for transmissions of duplicated packets.
It has been recognised that another type of antenna that may be used for wireless transmission by a device is a directional antenna. When using the directional antenna, the transmission is typically “beam-formed” into a particular direction towards an intended receiver instead of a general transmission broadcast in every direction when using an omni-directional antenna. Thus, by using directional beam-forming, transmitting devices are typically able to extend their range towards intended receiver devices, thereby establishing direct communication without increasing transmission power or using intermediate devices for relaying data. The range is typically extended without increasing transmission power due to the fact that the transmission energy is concentrated toward a particular direction. Apart from beam-forming during transmission, the device may also beam-form in a particular direction during reception. Beam-forming in a particular direction during reception typically increases the gain of the receiver device in that particular direction and hence typically enhancing reception. In addition, multi-path interference arriving at the receiver device from the non-intended directions may be filtered away. This may increase the signal-to-noise ratio to improve reception.
Another advantage of using directional beam-forming is better spatial re-use of the wireless medium. Since receiver devices may beam-form their receivers in the direction of their respective intended sender devices, the respective transmissions are typically carried out without causing interference at neighbouring receiver devices. This may improve spatial reuse of the wireless medium since the neighbouring receiver devices typically do not require waiting for the beam-form transmissions to be completed before receiving their own data packets.
However, having discussed the above advantages of directional beam-forming over using an omni-directional antenna, one problem of using directional beam-forming is a “device deafness” issue. The deafness issue typically refers to a situation when a device appears to be “deaf” and does not respond to any incoming communication packet. This may occur when the reception antenna of the receiving device is beam-formed in an intended direction of a transmitting device. Thus, the receiving device is typically unable to receive other transmissions sent from other devices disposed in other directions. When no response or acknowledgement packets are received from the receiving device in relation to these other transmissions, the other devices are typically unable to determine whether the receiving device is busy or whether the transmitted communication packets have not reached the receiving device. The other devices typically continue re-sending the communication packets thus not utilising fully the wireless medium access resource. In the above event, the receiving device which is not responsive to incoming communication packets, other than those transmitted from its intended transmitting device, is termed as “suffering” from “device deafness”.
Another problem that may arise when using directional beam-forming is how a transmitting device determines the direction of an intended receiving device. The problem also applies to how a receiving device determines the direction of the transmitting device to beam-form its receiver. Although there are currently some solutions to address the above problem, further problems may arise with each of these solutions. One of these solutions is to assume prior knowledge of the relative directions of the receiving device and of the transmitting sender device. One problem that may arise from this assumption is that mobile devices typically move and rotate on a frequent basis. Therefore, the prior knowledge may become obsolete and typically requires constant updating.
Another of the above solutions is to use an external positioning device (e.g. a Global Positioning System or GPS device) or to use the capability of the transmitting/sending device to perform real-time ranging and location-positioning measurements. However, one problem that may arise is that external positioning devices are typically expensive. As for real-time ranging and location positioning measurements, distance calibration is typically required to be performed by the device and the calibration is typically both time- and power-consuming.
Yet another of the above solutions is to use the transmitting device to first use an omni-directional transmission of control signals to reserve the wireless medium access time for subsequent communication using directional beam-forming with the intended receiving device. As the control signals are sent via the omni-directional transmission, the transmitting device typically need not know the direction of the intended receiver in advance. The receiving device typically determines the direction of the transmitting device from the control signals sent via the omni-directional transmission using a Direction-of-Arrival (DOA) calculation and responds to the transmission using either a directional beam-forming or an omni-directional transmission. The transmitting device typically determines the relative direction of the receiving device using the DOA calculation based on the received response transmission. One problem that may arise is range limitation. As the medium access time reservation and relative direction calculations are typically initiated by the omni-directional transmission of the transmitting device, the receiving device must already be located within the omni-directional transmission range of the transmitting device. Thus, the range extension advantage of directional beam-forming is not harnessed and the above scenario does not address the situation of devices not being able to communicate with other devices outside their respective omni-directional transmission range.
Yet another of the above solutions is for the transmitting device to utilise directional beam-forming to transmit a control signal to reserve the wireless medium access time for subsequent communication with its intended receiving device. As the transmitting device typically has no prior knowledge of the relative direction of the intended receiving device, the transmitting device transmits the control signal in a rotational manner such that the directional beam-forming transmission covers an entire 360°. However, one problem that may arise is that the sending of multiple duplicated control packets in the above manner is typically inefficient and typically degrades performance of the devices.
Hence, there exdsts a need for a method and system of wireless directional beam-forming transmission to address at least one of the above problems.